Abstract: Using the Devaney chaos theory，designd a compound chaos mapping as the encryption function，and have proven that the track is non-periodic for the initial value of finite decimal.It designs an encryption algorithm successively according to this，and realizes the encryption for sound documents.Afterward the simulation experiment has been carried on，it realized the key sensitivity analysis，the statistical analysis，as well as the correlation analysis of definite text and secret text.The experimental result proves that this system has the good cryptology performance，produces the large key space，meanwhile，it has good avalanche effect，resists exhaustion and the statistical analysis effectively.